1. Field of the Invention
The present invention relates to a coating method, a liquid supplying head and a liquid supplying apparatus.
2. Description of the Prior Art
An ink-jet head (liquid supplying head) is provided with a nozzle plate which has a plurality of minute nozzle holes mutually spaced apart with a narrow spacing left therebetween. The ink-jet head is designed to perform printing operations by ejecting ink droplets from apertures (ink-ejecting apertures) formed at one side of the nozzle holes and landing the ink droplets on a printing paper. In such an ink-jet head, once ink is adhered to a surface of the nozzle plate at the side where the ink-ejecting apertures lie, the flight trajectory of the ink droplets ejected next time becomes flexed under the influence of surface tension or viscosity of the adhered ink. This makes it difficult for the ink droplets to be landed on target spots. Taking this into account, an attempt has been made to form a liquid-repellent coat which consists of a fluorine-based resin or the like. In this attempt, the liquid-repellent coat is formed on an ink ejecting aperture-side surface of the nozzle plate, and further on a predetermined region (which is adjacent to the ink ejecting aperture) of an inner surface of each nozzle hole. This type of liquid-repellent coat is formed in the following manner, as taught in Japanese Laid-open Patent Publication No. 1995-125220 for example.
A nozzle plate is prepared first, and a photosensitive resin film which is curable by irradiation of light is laminated on the opposite surface of the nozzle plate from ink-ejecting apertures. Subsequently, the laminated resin film is heated while applying pressure on the film. Thus, the photosensitive resin film is heat-and-pressure bonded to the rear surface of the nozzle plate, and at the same time those parts of the photosensitive resin film facing to the nozzle holes are caused to enter the individual nozzle holes.
Then, ultraviolet rays are irradiated onto the photosensitive resin film to cure the latter. Subsequently, the nozzle plate is dipped and agitated in an electrolysis solution which contains nickel ions and a fluorine resin dispersed by electric charges. In this way, a eutectoid plating layer is formed on the part of the nozzle plate not covered with the photosensitive resin film, i.e., on the ink ejecting aperture-side surface of the nozzle plate and on the inner surface parts of the nozzle holes adjacent to the ink-ejecting apertures. Finally, the photosensitive resin film is dissolved and removed by use of a solvent, after which the nozzle plate is heated at a temperature no greater than the melting point of the fluorine resin contained in the eutectoid plating layer.
Through the process described above, a liquid-repellent coat is formed on the ink ejecting aperture-side surface of the nozzle plate and on the predetermined region (which is adjacent to the ink-ejecting apertures) of the inner surface of each nozzle hole. However, this method involves following problems.
The method described above employs the photosensitive resin film. Therefore, even for the regions of the nozzle plate that do not require formation of the liquid-repellent coat, it is required to perform the steps of: bonding a photosensitive resin film to a nozzle plate by heat and pressure; curing the photosensitive resin film; and dissolving and removing the photosensitive resin film.
Not only do these steps involve complexity but also they require installations for carrying out each of the steps. In addition, the photosensitive resin film is inherently expensive, which in turn increases production costs.